Prosecutors at the International Criminal Court say they have "reasonable basis" to believe the United States committed "war crimes" by torturing prisoners in Afghanistan.

The U.S. military subjected at least 61 detainees in Afghanistan to "torture, cruel treatment, [and] outrages upon personal dignity," an initial investigative report said on November 14.

A further 27 people were tortured by the CIA, it said, with the majority of the alleged crimes occurring between 2003 and 2004 when President George W. Bush was in office.

The United States never ratified the treaty establishing the court, but because the alleged abuses occurred in countries that ratified the treaty -- Afghanistan, Poland, Lithuania and Romania -- the court has jurisdiction.

The report claims the crimes were not "isolated," but were part of "approved interrogation techniques" aimed at extracting "actionable intelligence" from detainees.

The court was established in 2002 to prosecute war crimes, crimes against humanity, and genocide. It said it would decide "imminently" whether to commence a full investigation.

U.S. State Department spokeswoman Elizabeth Trudeau said the United States did not believe a full investigation is "warranted or appropriate."

"The United States is deeply committed to complying with the law of war, and we have a robust national system of investigation and accountability that more than meets international standards," Trudeau said.

President-elect Donald Trump has said he would reinstate waterboarding -- a torture method that simulates drowning that was abandoned by the Obama administration -- and techniques that are "a hell of a lot worse" to obtain information from "terrorists."